When a terminal like a personal computer or a smart phone gives print instructions to an image forming apparatus like a MFP (Multi-Functional Peripheral) which is connected to the terminal through a network, the terminal needs IP (Internet Protocol) address of the MFP for sending a print job to the MFP. There is a way or system for searching for a MFP located in the same subnetwork (hereinafter, also referred to as a subnet), which is called multicast DNS (Domain Name System). The multicast DNS makes a terminal possible to display a list of MFPs existing in the same subnet, which allows a user to use a desired MFP easily just by selecting it from the list.
However, in a system such that a terminal and a nearby MFP are not located in the same subnet, the terminal may not find the MFP even if using the multicast DNS. There is a method of using a server (DSS: Discovery Service Server) to register and manage MFPs existing in various subnets, which is called BMLinkS (registered trademark). This method makes a terminal possible to search for a MFP in a subnet different from the subnet where the terminal exists, by inquiring of the server the MFP. As another technique which makes it possible to search for a MFP in a subnet different from the subnet where the terminal exists, Japanese Unexamined Patent Publication (JP-A) No. 2009-289041, which corresponds to United States Patent Application Publication No. US2009/0300175A1, discloses a method of preparing servers for respective subnets and making these servers cooperate to send information of MFPs to a terminal.
Moreover, JP-A No. 2001-331392 discloses the following network-device control apparatus. The network-device control apparatus includes a searching section that uses devices connected to a network as a search range with a broadcast packet or a subnet broadcast packet, and searches for a device; a monitoring section that monitors arbitrary packets forwarded in the network; a packet filtering section that extracts a print-job packet from the monitored packets; a determining section that determines whether the forwarding address of the extracted print-job packet is within the subnet where the network-device control apparatus exists; and an adding section that adds a subnet other than the subnet of the network-device control apparatus to the search range on the basis of the determination result.
The BMLinkS makes a terminal possible to search for a MFP existing in a subnet which is different from the subnet where the terminal exists. However, the BMLinkS needs a DSS having a specific function, to be located in a network, and it is not easy to search for a MFP in a different subnet with this technique. The technique disclosed in JP-A No. 2009-289041 (which corresponds to US2009/0300175A1) needs a server to be prepared for each subnet and further needs a terminal, which gives print instructions, to have a function to send search packets to MFPs on the basis of MFP information received from the servers, and it is not easy to search for a MFP in a different subnet with this technique. Furthermore, the technique disclosed in JP-A No. 2001-331392 is given on the assumption that a terminal is always connected to one subnet. Accordingly, since a terminal temporarily linked to a subnet, such as a portable terminal and a terminal at the time of a business trip, cannot monitor packets in advance, the terminal cannot use the above technique. Moreover, similarly to the technique disclosed in JP-A No. JP 2009-289041, the technique disclosed in JP-A No. 2001-331392 needs a terminal to have the above function, and only limited terminals can use the technique.